Pick the rated current just above the load or the cable rating, a breaking capacity above the fault level at that point (higher near a big transformer), 4 pole where the neutral must be switched, and a microprocessor release where you need fine adjustable settings.
1. Rated current
The frame size (for example 100, 250 or 630 A) is the largest current the MCCB can carry; the setting (Ir) is the trip level you choose. Set it at or just above the load current and never above the current the outgoing cable can carry.
2. Breaking capacity (kA)
The MCCB must break the largest fault current possible at its location. Close to the transformer this can be high. A rough estimate: transformer full-load current ÷ impedance.
| Transformer | Impedance | Approx. fault level at its LV terminals |
|---|---|---|
| 250 kVA | 4% | 8.7 kA |
| 500 kVA | 4.5% | 15.5 kA |
| 1000 kVA | 5% | 27.8 kA |
| 1600 kVA | 6.25% | 35.6 kA |
Choose an MCCB whose rated breaking capacity is above this figure. Further from the transformer, cable impedance lowers the fault level, so smaller kA ratings may be enough on sub-feeders. Your consultant or electrician confirms the fault level.
3. Poles
3 pole for three-phase loads; 4 pole where the neutral must also be isolated, as at incomers and with generator changeover.
4. Release type
A thermal-magnetic release is simple and economical, with fixed or limited adjustment. A microprocessor (electronic) release gives finely adjustable long-time, short-time and instantaneous settings, earth-fault protection and better coordination: the usual choice at main incomers.
Accessories
Add as needed: auxiliary and trip-alarm contacts for indication, a shunt trip for emergency stop, an undervoltage release, a rotary handle for panel-door operation, and spreaders or terminal covers for cable termination.
MCCBs we supply
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Send us the rating, the load or a photo of the nameplate on WhatsApp, and we will confirm the right model, availability and rate.
Values are typical guidance for Indian 230 V single-phase and 415 V three-phase supplies. Always follow the equipment nameplate, the manufacturer's instructions and your licensed electrician, who is responsible for the final selection and installation.